Method of making a cigarette filter tow



' Feb. 18, 1969 R. c. HARRINGTON, JR, ETAL 3,428,723

METHOD OF MAKING A CIGARETTE FILTER TOW Filed Sept. 15, 1965 CIGARETTE WRAPPER FILTER WRAPPER 46 ROBERT c- HARRINGTON JR- 0O ROBERT L- AMMONS og g cw 68 INVENTORS J! a v 58 T fi'ZM/M FIG 5 ATTORNEYS United States Patent 1 Claim ABSTRACT OF THE DISCLOSURE A process is provided for producing a cigarette filter tow which comprises spinning a solution of cellulose acetate into a core of filaments without exerting drawing tension and an outer layer of filaments with drawing tension thereby resulting in a tow of irregularly shaped unoriented filaments encased within an outer layer of smooth oriented filaments.

This invention relates to the manufacture of new cellulose organic acid ester filamentous masses that are especially well adapted for forming superior tobacco smoke filter. More particularly, the invention relates to the manufacture of highly crimped or irregular filaments and fibers for use in forming cigarette filters, and to novel processes of spinning these filamentous masses.

The filaments and fibers that are presently being used to form tobacco smoke filters are formed primarily from cellulose acetate or other like organic solvent soluble materials by the dry or evaporative type spinning process. In all modifications of the dry or evaporative spinning process heretofore known or practices in producing such filter fibers the fine streams of spinning solution immediately upon leaving the spinnerette orifices, and before any substantial solidification has taken place, are subjected to a certain amount of tension which is normally imposed by a positive drawing of the filaments from the spinnerette. This tension causes substantial elongation of the fine streams of spinning solution before and during trasforrnation into self-sustaining filaments. The imposed tesion and the internal strain set up in the filamentous structures at the time of their birth bring about substantial orientation of the molecules along the filament or fiber axis. The formed filaments are, therefore, inherently straight and can be drawn or otherwise arranged in a substantially parallel relationship to form a tow which is adaptable for use in the manufacture of cigarette filter elements.

However, as is well known in the tobacco smoke filter art, the parallel fibers from which the filter is to be formed must be crinkled or crimped if the best possible filtering action is to be obtained. Thus it has always been necessary to subject the substantially straight filaments or fibers of the filter tow to any of several after-treatments to produce the desired crimps. For instance, the crimps may be produced mechanically by means of intermeshing gear like elements, by means of a stuffer box type crinkler, or by twisting the fibers, setting the twist and then untwisting.

As will be apparent, not only does this additional step of crimping otherwise parallel fibers require a separate processing step which is both time consuming and expensive, but the crimped tow must be handled very carefully during shipment and formation of the filter elements or the fibers will be stretched and the crimps thus removed. This special handling problem, therefore, represents a very decisive disadvantage in using such crimped tow materials in manufacturing tobacco smoke filters.

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Furthermore, even though the drawn fibers have been crimped it has often been found necessary to add certain types of finely-divided additives to the filter tow as it is being formed into tobacco smoke filters to break up the continuous channels or interstices that otherwise extend completely through the filter from the smoking tobacco to the outer end of the filter tip. Without the addition of hese additives certain undesirable solid and gaseous constituents of the tobacco smoke would be drawn directly through the filter via these continuous channels between the parallel fibers without any filtering taking place. Again it is apparent that the addition of these additives requires another process step that unduly complicates and increases the expense of producing tobacco smoke filters.

In an effort to avoid the necessity of crimpinga filter tow material and placing an additive therein during the formation of tobacco smoke filters, it has been proposed that fibers be used having irregular shapes and of nonuniform denier. It was found that one method by which such irregular fibers could be formed was through the use of a free-fall spinning technique. In this free-fall spinning process the fine streams of spinning solution immediately upon leaving the spinnerette orifices are permitted to fall under no draft or tension until they are solidified into self-sustaining filaments. This operation produces fibers having a very rough surface with an uneven crosssection and randomly spaced permanent crinkles or crimps. This type of fiber configuration is ideal for use in tobacco smoke filters since its irregularity assures that no direct channels or interstices will exist through the filter. Unfortunately, however, filter tows formed from free-fall spun fibers cannot be readily processed in the usual manner because they are:

(l) Comparatively weak;

(2) Cannot be formed into filter tows of uniform denier;

(3) Tend to cling to each other, and cannot be removed from a bale or other package;

(4) Cannot be readily opened as is required in manufacturing tobacco smoke filters to provide the required draw or pressure drop characteristics.

Therefore, even though drafted parallel fibers have certain disadvantages as hereinabove enumerated they nevertheless are easier to handle and work into tobacco smoke filters. Thus, they have until now continued to be the filamentous mass from which most filter tow material is formed.

According to this invention it has now been found that a filamentous mass can be produced which combines all the desirable characteristics of both the drafted and freefall spun fibers while at the same time eliminating each of their undesirable traits. This continuous, highly crimped, filamentous filtermass is produced by using a novel method and apparatus whereby free-fall spun fibers are encased within a sheath or jacket formed from drafted substantially parallel fibers. This combination bundle of fibers can easily be processed into a filter tow or used as produced to form tobacco smoke filters which exhibit superior fabrication and filtering properties over like filter made from only a drawn or free-fall spun filamentous mass.

Therefore, an object of. this invention is to provide a filamentous mass consisting of an outer casing of substantially parallel drawn spun fibers with a core of irregularly formed free-fall spun fibers.

Another object of this invention is to provide a filter medium characterized by the combination of a bundle of looped, entangled and rough surfaced fibers combined with crimped, essentially parallel fibers.

Still another object of this invention is to provide an easy processable and highly efiicient tobacco smoke filter consisting of a core formed from free-fall spun fibers en- 3 closed with a sheath formed from draw spun parallel fibers.

Yet still another object of this invention is to provide a new method and apparatus for spinning thermoplastics from solutions in organic solvents so as to produce a combination filter tow having a core of highly crinkled and irregular continuous filaments which exhibit no preferential molecular orientation along the filament axis, and an outer sheath surrounds the core filaments formed of uniform continuous filaments which exhibit preferential molecular orientation along the filament axis.

A further object of this invention is to provide a filter tow that includes orientated, entangled and rough surface fibers which can be processed and handled in substantially the same manner as tows formed from parallel, crimped fibrous arrangements.

A special object of this invention is to provide a cigarette filter with high removal efiiciency which has a core formed from cellulose acetate free-fall spun fibers surrounded by an outer thin layer of cellulose acetate draw spun fibers, and to the process of producing such cigarette filter fibers.

These and other objects and advantages of this invention will be more apparent upon reference to the following description, specific working examples, appended claims and drawings wherein:

FIGURE 1 is a semi-schematic drawing of one embodiment of the process for the preparation of filaments of this invention from a spinning solution;

FIGURE 2 is a cross section taken along the line 2-2 of FIGURE 1 showing the face of the double spinnerette head;

FIGURE 3 is a greatly magnified view of a plurality of free-fall spun fibers produced in accordance with this invention and showing the characteristic irregular shapes thereof;

FIGURE 4 is a perspective view, with portions thereof cut away, of a cigarette with a filter made in accordance with this invention;

FIGURE 5 is a cross-sectional view taken along line 55 of FIGURE 1.

As mentioned briefly hereinabove, the novel filamentous products of this invention are particularly well adapted to be formed by the dry or evaporative spinning process wherein one or more solutions comprising essentially a thermoplastic filament-forming material dissolved in a volatile organic solvent or solvent mixture is extruded in the form of fine streams into an evaporative atmosphere under such conditions that a portion of the extruded material is subjected only to compressive force until it sets in the form of self-sustaining filaments; i.e., that portion of the solution is extruded under (1) sufiicient pressure or at a sufiiciently high jet velocity that the filaments formed are pushed away from the extrusion zone by subsequently extruded material issuing from the jets, and (2) in the absence of any draw tension on the freshly formed filaments until they are substantially set. The other or second portion of the extruded material is subjected to a draw tension in a normal manner so that the freshly formed filaments are substantially straight and of uniform size. Ideally these drawn filaments are positioned around and encase the free-fall formed filaments in a conduit like outer enclosure.

With continued reference to the accompanying figures wherein like reference numerals designate similar parts throughout the various views, and with initial attention directed to FIGURE 1, reference numeral is used to generally designate a filamentous mass forming apparatus constructed in accordance with the concepts of the present invention. This forming apparatus 10 is somewhat similar in appearance to a conventional spinning apparatus and consists of a spinning'cabinet 12 which has a special type of spinnerette 14 mounted at the top thereof. As can be seen, the space back of the spinnerette head 16 is divided by a U-shaped partition 18 into two separate regions or compartments 20-22. Each of these compartments 20 and 22 communicating with a separate set or group of orifices 24-26 which may or may not be of the same size. As more clearly seen in FIGURE 2, the outer orifices 24 are arranged in a circular or other suitable configuration around the inner orifices 26.

Separate feed lines or conduits 28-30 are provided for supplying the spinning solution, or solutions as the case may be, from a mixing and storage container 32 to the two compartments 20 and 22. Both of these feed lines are provided with a pump 34-36 for supplying the spinning solution to the various compartments under the proper pressure for achieving the desired filamentous mass. For reasons that will be more fully explained hereinafter, the pressure within the compartment 22 is normally maintained at a higher level than that in compartment 20.

The lower or bottom portion of the spinning cabinet 10 is provided with an opening 38 which is located below the face plate 16 of the spinnerette 14. A take-up wheel 40 is located immediately outside the opening 38 for both maintaining proper tension on the filaments of this mass that are spun through the outer orifices 24 of the spinnerette 14, and for removing the combined filamentous mass produced. For purposes of speeding the curing of the wet filamentous mass as it leaves the spinnerette head and moves along the longitudinal axis of the spinning cabinet 10 toward the opening 38, a curing gas can be forced into the spinning cabinet through inlet conduit 42 and withdrawn from the cabinet by an outlet conduit 44. This produces a desirable up-draft of curing gas within the cabinet 10.

The operation of the filamentous mass forming apparatus 10 may be described substantially in the following manner. An organic solvent-soluble thermoplastic spinning solution such as, for example, cellulose acetate from which the filamentous mass is to be formed is placed in the storage container 32. The pumps 34 and 36 are then energized thereby forcing the spinning solution from the container 32 through the conduit feed-lines 28-30 into the compartments 20-22, respectively. The pressurized spinning solution within each of the compartments 20-22 is forced through the orifices 24-26 and into the chamber within the spinning cabinet 12. Here within the spinning cabinet the liquid spinning solution is cured by the curing gas flowing from conduit 42 to conduit 44 thereby forming a self-sustaining filamentous mass as represented by numeral 46. This filamentous mass, which may be randomly bonded together at the point where they touch so that the draw spun and free-spun fiber are integral parts, is further gathered together at the lower end of the spinning cabinet 12 and passes through the opening 38 onto the take-up roller 40. From the roller 40 the combination filamentous mass 46 is moved by a conveyor or like unit 48 through suitable dryer apparatus 50, if such is required, and is packed as a tow material 52 by a baler unit 54.

In order to form the combination tow material 52 of this invention, the exit or jet velocity of the spinning solution leaving both the orifices 24-26 must be properly adjusted in reference to the speed with which the take-up wheel 40 is removing the filamentous mass 46 from the spinning cabinet 12. In all cases the jet velocity of the spinning solution leaving the outer orifices 24 must be low enough so that the take-up wheel will exert a suitable tension or draw pressure on the filaments 56 being formed. This imposed tension and the resultant internal strain set up in the filaments 56 at the time of their birth brings about substantial orientation of the molecules along the filaments axis. As is well known, this condition results in the formation of inherently straight filaments having very smooth outer surfaces which, when formed into a tow material, will produce a substantially parallel fibrous arrangement.

On the other hand, the jet velocity of the spinning Solution leaving the inner orifices 26 must be high enough so that the filaments 58 will free-fall in reference to the speed with which the outer filaments 56 are moving and the filamentous mass 46 as a whole is being withdrawn from the spinning cabinet 12. This high jet velocity re sults in the filaments 58 being formed under no pressure other than that exerted by the pushing of the spinning solution subsequently extruded and the weight of each filament itself, which is nill.

The filaments 58 so produced are characterized by a combination of properties unique in the tobacco smoke filter art. For example, they are very irregularly crinkled with the crimps extending in three dimensions as distinct from mechanically imposed crimps produced heretofore which lie in but one plane. When viewed under magnification the filaments 58 exhibit rough, unsymmetrical surfaces characterized by deeply cut, irregular, disconnected pits or channels along with corresponding peaks or ridges. These cuts or channels may extend substantially through the filaments and when such corresponding surface characteristics of two or more adjacent filaments occur sideby-side, as is often the case and is illustrated at 60 in FIGURE 3, a blocking of the interstices or channels that might otherwise exist along the longitudinal axis of the filamentous mass is accomplished. Furthermore, at intervals along the length of the filaments 58 web-like formations 62 are found which appear to be composed of one or more loops in the fiber.

These physical characteristics of the filaments 58 have marked effects on the filter properties of the bundles or masses of fibers which make up the center or core portion 64 of the tobacco smoke filter 66 illustrated in FIG- URE 4. The effects of these looped, entangled and rough surfaced filaments is to give a surprisingly high filtering efliciency for certain tobacco smoke constituents. This, it is believed, can be attributed in great measure to the rough surface configuration of fine protuberances which efiectively blocks the flow of such solid or liquid tobacco smoke constituents as tar and nicotine through the filter but permits the free flow of the gaseous tobacco constituents.

The presence of the outer sheath or enclosure 68 of drawn filaments 56 around the free-fall spun fibers 58, as illustrated in FIGURE 5, is of utmost importance since they permit the combination filamentous mass 46 to be handled in a conventional manner on existing tobacco smoke filter forming equipment. These drawn filaments 56 impart to the total filamentous mass 46 the strength required and which is totally absent in the free-fall spun filaments 58 per se.

A further understanding of the invention will be had from a consideration of the following examples that may be used in actual commercial practice and are set forth to illustrate certain preferred embodiments.

Example 1 A combined filamentous mass was spun in substantially the manner illustrated in FIGURE 1 to give a combination fiber. A plurality of filter rods were then made from their combination fibers to give a filter tow of approximately 90,000 total denier. The draw spun fibers in this tow was approximately 5 denier/filament (d.f.) and of 30,000 total denier. The remainder of the tow was made up of the free-fall spun fibers produced using a 19.03 jet.

The filter tow was formed into filter rods in a conventional manner except that no plasticizer or other bonding material was required. These filter rods had a circular shape with a diameter substantially equal to a standard cigarette. The filter rods were cut to form standard size (15 mm.) filter elements and these elements were attached to the tip of commercially available king-size cigarettes.

To evaluate the properties of these filter elements a selected number were tested and analyzed for pressure drop and tar removal factors. The pressure drop test was made with a U tube manometer. Thus, pressure drop as used hereinbelow refers to the inches of water required to obtain an air flow of 1050 cc. of air-per-minute through a 15 mm. filter tip. This pressure drop in the present example was found to be 2.5. The percent tar removal accomplished by the filter tips was determined by smoking the king-size filter tipped cigarettes on a smoking machine described in U.S. Patent No. 2,881,769. A 2- second puff was made each minute. For comparison purposes, similar tests were made on the same type king size cigarettes containing no filter tip. The percent tar removal given hereinbelow is the ratio of the weight of tars and nicotine passed by the standard brand cigarette without filter tips minus the weight of tars and nicotine passed by the standard-brand cigarettes with filter tips. In the present example the tar and nicotine removal was 52 percent.

As a comparison, the filter plug made with 5 d./f., 30,000 total denier conventional draw spun and crimped tow had a pressure drop of 1.6 inches and gave only 16 percent tar and nicotine removal.

'Example 2 Filter tips were again made and tested as described in Example 1 except that the draw spun fibers were 5 d./f. and of 20,000 denier. The remaining portion of the 90,000 total denier filter tip was free-fall spun tow made by using a 19.03 jet.

The pressure drop for a 15 mm. tip was 2.05, and the tar and nicotine removal was 45 percent.

Example 3 Filter elements were made from a combination tow of approximately 90,000 total denier in the manner described inExample l. The conventional draw spun filaments of the tow were of 5 d./f. and approximately 40,000 total denier. The remainder of the tow was free-fall spun fibers made by using a 19.03 jet.

The pressure drop for 15 mm. filter tips made of this combination tow was found to be 2.0, and the tar and nicotine removal was 48 percent.

Example 4 Filter elements were made from a combination tow of approximately 90,000 total denier in the manner described in Example 1. The conventional draw spun filaments of the tow were of 5 d./f. and approximately 50,000 total denier. The remainder of the tow was free-fall spun fibers made by using a 19.03 jet.

The pressure drop for 15 mm. filter tips made of this combination tow was found to be 1.8, and the tar and nicotine removal was 29 percent.

Example 5 Filter elements were made from a combination tow of approximately 60,000 total denier in the manner described in Example 1 except that a plasticizer was used to bond the tow. The conventional draw spun filaments of the tow were of 5 d./f. and approximately 25,000 total denier. The remainder of the tow was free-fall spun fibers made by using a 19.03 jet.

The pressure drop for 15 mm. filter tips made of this combination tow was found to be 3.0 inches, and the tar and nicotine removal was 56 percent.

Example 6 A combination tow made of 50 percent by weight 5 d./f. (30,000 total denier) conventional draw spun filaments and 50 percent free-fall spun filaments from a 75- 03 jet was calendered into a batting which was then processed into filter elements in substantially the manner described in Example 1. The pressure drop for 15 mm. filter tips made of this combination tow was found to be 1.4 inches, and the tar and nicotine removal was 36 percent.

From the foregoing it is seen that not only does the present invention make possible the handling and processing of free-fall spun fibers at a speed and in a manner heretofore impossible, but the use of these free-fall spun fibers in tobacco smoke filters gives superior filtration properties. Furthermore, these combination free-fall and conventional spun fibers do not require the addition of finely-divided additives to block the filter interstices nor the use of a plasticizer for bonding the fiber into a cigarette filter. Needless to say, in view of the commercial importance of tobacco smoke filters made from various types of spinning solutions, this invention is of greatest immediate value when applied to the production of these type of filter elements.

As will be noted from the above description of the process, apparatus and products of this invention, various modifications and changes are readily apparent. For example, the spinnerette head can be supplied with two different spinning solutions thus permitting the free-fall spun fibers to be of one material while the conventional spun sheath fibers are of another. The number, shape, size and position of the orifices in the spinnerette can also be varied or changed to give filamentous mass having different fiber ratios so long as the draw spun fiber sufficiently enclose the inner bundle of free-fall spun fibers as to permit the combination fibers to be easily handled and used. Furthermore, the overall size of the spinnerette head can be increased to thereby spin a single filamentous mass that is the proper size for use as a cigarette filter thus alleviating the need for combining several smaller combination fibers to form a filter tow or web.

This invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

What is claimed and desired to be secured by United States Letters Patent is:

1. A method of producing a cigarette filter tow having a core of irregularly shaped fibers substantially free of molecular orientation along the axis of the cigarette filter tow encased in an outer layer of fibers having relatively smooth outer surfaces and molecularly oriented along the axis of the cigarette filter tow said process comprising the steps of forming said core of irregularly shaped fibers by extruding an organic solvent solution of cellulose acetate into a plurality of filaments which are subjected to substantially no drawing tension, simultaneously forming said outer layer by extruding additional organic solvent solution of cellulose acetate around said core into a plurality of filaments which are subjected to sufficient drawing tension to cause molecular orientation along the fiber axis, and collecting the resulting said cigarette filter tow.

References Cited UNITED STATES PATENTS 2,904,953 9/1959 Groombridge et a1. 264168 2,968,834 1/1961 Groombridge et a1. 264-103 3,080,611 3/1963 Jarrett et al 264--207 JULIUS FROME, Primary Examiner.

HERBERT MINTZ, Assistant Examiner.

US. Cl. X.R. 264168, 171, 208 

